1. Field of the Invention
This invention relates to an improved lance construction for supplying pressurized fluids beneath the surface of molten metal in a refractory lined refining vessel, and more particularly as applied to a method for oxygen refining of molten steel wherein a stream of oxygen-bearing gas is introduced beneath the surface of the molten steel in an electric arc furnance or similar refining vessel. A cooling gas, wich may be a combustible hydrocarbon, is introduced simultaneously with the oygen-bearing gas to act as a shield or shroud gas so as to decrease consumption of the submerged end of the lance.
2. Description of the Prior Art
The theoretical advantages of oxygen refining by means of a submerged lance or tuyere have been known for many years. However, attempts to practice this concept on a commercial scale have encountered a number of problems which have prevented full realization in actual practice of the theoretical advantages.
Among the problems inherent in injection of commercially pure oxygen or oxygen-enriched air (hereinafter referred to for convenience as "oxygen-bearing gas" ) through a submerged lance or tuyere are premature failure of the lance due to infiltration of molten metal and solidification thereof behind the tip of the lance, rapid consumption of the submerged lance tip and severe erosion of the refractory lining of the furnace or other refining vessel adjacent the discharge end of the lance or tuyere. Although the prior art has addressed itself to the solution of some or all of these problems, none of the alleged solutions has been entirely satisfactory to the best of applicants' knowledge.
British Pat. No. 882,676, published in November 1961, disclosed the concept of introducing an oxygen-containing gas below the surface of molten ferrous metal through a lance consisting of an inner steel tube surrounded by a concentric steel tube of greater diameter, with a combustible gas being passed through the annular space between the tubes. A similar disclosure was contained in French Pat. No. 1,450,718 published Aug. 26, 1966, wherein oxygen and a combustible hydrocarbon gas were injected at relatively low pressures. The use of a combustible gas surrounding the oxygen gas stream was found to cool the region adjacent the discharge end of the lance or tuyere and to decrease the reaction rate of the oxygen discharged therefrom. This in turn decreased consumption of the submerged lance tip and erosion of the refractory lining of the refining vessel adjacent the lance tip.
Subsequent to the above disclosures, considerable attention has been devoted to improvements on the basic concept of oxygen refining by means of submerged lances or tuyeres and in improvements in lance construction. Among the many United States Patents in this field, reference may be made U.S. Pat. Nos. 3,330,645; 3,703,279; 3,706,549; 3,722,814; 3,751,019; 3,781,001; 3,794,308; 3,819,165; 3,829,073; 3,851,866; 3,897,048; and 3,951,643.
Patents such as U.S. Pat. Nos. 3,330,645; 3,819,165 and 3,829,073 disclose a coaxial tuyere arrangement wherein oxygen is blown through a center tube, hydrocarbon or other cooling fluid is introduced through an annular porous member or through a plurality of channels of small cross sections.
Patents such as U.S. Pat. Nos. 3,703,279 and 3,706,549 apparently assume that erosion of the refractory lining and consumption of the lance tip cannot be prevented and provide an erodible tuyere comprising coaxial inner and outer tubes of constant cross section (in the case of U.S. Pat. No. 3,703,279 ) or arrange a relative proportioning of oxygen and hydrocarbon gas flows in such manner that the lance or injector tip (positioned in the bottom of the reaction vessel) is consumed at a rate substantially the same as the refractory lining (in the case of U.S. Pat. No. 3,706,549 ).
Patents such as U.S. Pat. Nos. 3,751,019 and 3,794,308 provide fluid cooling for the lance tip exposed to molten metal.
U.S. Pat. No. 3,897,048 discloses a tuyere assembly comprising coaxial tubes wherein fuel only may be pumped through an outer annular space, oxygen only may be blown through an inner annular space, and valving is provided in order to blow fuel only, oxygen only, oxygen and fuel, or an inert gas through a central tube.
U.S. Pat. No. 3,951,643 discloses a coaxial tuyere arrangement in an electric arc furnace pivotal between a first position and a second position wherein the angle at which the tuyere projects through the furnace wall can be adjusted when the tuyere is installed.